Systems and methods for terrestrial reuse of cellular satellite frequency spectrum in a time-division duplex mode

ABSTRACT

A space-based component, such as a satellite, is configured to receive wireless communications from radiotelephones in a satellite footprint over an uplink satellite radiotelephone frequency, and to transmit wireless communications to the radiotelephones over a downlink radiotelephone frequency. An ancillary terrestrial network, that may include one or more ancillary terrestrial components, is configured to transmit wireless communications to, and receive wireless communications from, the radiotelephones over the downlink satellite radiotelephone frequency in a time-division duplex mode. By terrestrially transmitting and receiving wireless communications over the downlink satellite radiotelephone frequency in a time-division duplex mode, interference at the space-based component and/or at the gateway, by the ancillary terrestrial network and/or the radiotelephones due to terrestrial reuse of cellular satellite frequency spectrum, may be reduced or eliminated.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.10/730,660, filed Dec. 8, 2003, entitled Systems and Methods forTerrestrial Reuse of Cellular Satellite Frequency Spectrum In aTime-Division Duplex Mode, which itself is a continuation-in-part ofU.S. application Ser. No. 10/074,097, filed Feb. 12, 2002 (now U.S. Pat.No. 6,684,057), entitled Systems and: Methods for Terrestrial Reuse ofCellular Satellite Frequency Spectrum, which itself claims the benefitof provisional Application No. 60/322,240, filed Sep. 14, 2001, entitledSystems and Methods for Terrestrial Re-Use of Mobile Satellite Spectrum,all of which are assigned to the assignee of the present application,the disclosures of all of which are hereby incorporated herein byreference in their entirety as if set forth fully herein.

FIELD OF THE INVENTION

This invention relates to radiotelephone communications systems andmethods, and more particularly to terrestrial cellular and satellitecellular radiotelephone communications systems and methods.

BACKGROUND OF THE INVENTION

Satellite radiotelephone communications systems and methods are widelyused for radiotelephone communications. Satellite radiotelephonecommunications systems and methods generally employ at least onespace-based component, such as one or more satellites that areconfigured to wirelessly communicate with a plurality of satelliteradiotelephones.

A satellite radiotelephone communications system or method may utilize asingle antenna beam covering an entire area served by the system.Alternatively, in cellular satellite radiotelephone communicationssystems and methods, multiple beams are provided, each of which canserve distinct geographical areas in the overall service region, tocollectively serve an overall satellite footprint. Thus, a cellulararchitecture similar to that used in conventional terrestrial cellularradiotelephone systems and methods can be implemented in cellularsatellite-based systems and methods. The satellite typicallycommunicates with radiotelephones over a bidirectional communicationspathway, with radiotelephone communication signals being communicatedfrom the satellite to the radiotelephone over a downlink or forwardlink, and from the radiotelephone to the satellite over an uplink orreturn link.

The overall design and operation of cellular satellite radiotelephonesystems and methods are well known to those having skill in the art, andneed not be described further herein. Moreover, as used herein, the term“radiotelephone” includes cellular and/or satellite radiotelephones withor without a multi-line display; Personal Communications System (PCS)terminals that may combine a radiotelephone with data processing,facsimile and/or data communications capabilities; Personal DigitalAssistants (PDA) that can include a radio frequency transceiver and apager, Internet/intranet access, Web browser, organizer, calendar and/ora global positioning system (GPS) receiver; and/or conventional laptopand/or palmtop computers or other appliances, which include a radiofrequency transceiver.

Terrestrial networks can enhance cellular satellite radiotelephonesystem availability, efficiency and/or economic viability byterrestrially reusing at least some of the frequency bands that areallocated to cellular satellite radiotelephone systems. In particular,it is known that it may be difficult for cellular satelliteradiotelephone systems to reliably serve densely populated areas,because the satellite signal may be blocked by high-rise structuresand/or may not penetrate into buildings. As a result, the satellitespectrum may be underutilized or unutilized in such areas. The use ofterrestrial retransmission can reduce or eliminate this problem.

Moreover, the capacity of the overall system can be increasedsignificantly by the introduction of terrestrial retransmission, sinceterrestrial frequency reuse can be much denser than that of asatellite-only system. In fact, capacity can be enhanced where it may bemostly needed, i.e., densely populated urban/industrial/commercialareas. As a result, the overall system can become much more economicallyviable, as it may be able to serve a much larger subscriber base.Finally, satellite radiotelephones for a satellite radiotelephone systemhaving a terrestrial component within the same satellite frequency bandand using substantially the same air interface for both terrestrial andsatellite communications can be more cost effective and/or aestheticallyappealing, Conventional dual band/dual mode alternatives, such as thewell known Thuraya, Iridium and/or Globalstar dual modesatellite/terrestrial radiotelephone systems, may duplicate somecomponents, which may lead to increased cost, size and/or weight of theradiotelephone.

One example of terrestrial reuse of satellite frequencies is describedin U.S. Pat. No. 5,937,332 to the present inventor Karabinis entitledSatellite Telecommunications Repeaters and Retransmission Methods, thedisclosure of which is hereby incorporated herein by reference in itsentirety as if set forth fully herein. As described therein, satellitetelecommunications repeaters are provided which receive, amplify, andlocally retransmit the downlink signal received from a satellite therebyincreasing the effective downlink margin in the vicinity of thesatellite telecommunications repeaters and allowing an increase in thepenetration of uplink and downlink signals into buildings, foliage,transportation vehicles, and other objects which can reduce link margin.Both portable and non-portable repeaters are provided. See the abstractof U.S. Pat. No. 5,937,332.

In view of the above discussion, there continues to be a need forsystems and methods for terrestrial reuse of cellular satellitefrequencies that can allow improved reliability, capacity, costeffectiveness and/or aesthetic appeal for cellular satelliteradiotelephone systems, methods and/or satellite radiotelephones.

SUMMARY OF THE INVENTION

Some embodiments of the present invention allow a satelliteradiotelephone frequency to be reused terrestrially within the samesatellite cell in time-division duplex mode. In particular, someembodiments of the present invention include a space-based component,such as a satellite, that is configured to receive wirelesscommunications from radiotelephones in a satellite footprint over anuplink satellite radiotelephone frequency, and to transmit wirelesscommunications to the radiotelephones over a downlink radiotelephonefrequency. An ancillary terrestrial network, comprising one or moreancillary terrestrial components, is configured to transmit wirelesscommunications to, and receive wireless communications from, theradiotelephones over the downlink satellite radiotelephone frequency ina time-division duplex mode. By terrestrially transmitting and receivingwireless communications over the downlink satellite radiotelephonefrequency in a time-division duplex mode, interference at thespace-based component, by the ancillary terrestrial network and/or theradiotelephones due to terrestrial reuse of cellular satellite frequencyspectrum, may be reduced or eliminated.

In other embodiments of the present invention, the ancillary terrestrialnetwork also is configured to transmit wireless communications to, andreceive wireless communications from, the radiotelephones over theuplink satellite radiotelephone frequency in a time-division duplexmode. In yet other embodiments, the space-based component may beconfigured to receive wireless communications from the radiotelephonesand to transmit wireless communications to the radiotelephones over theuplink satellite radiotelephone frequency and/or the downlink satelliteradiotelephone frequency in a time-division duplex mode.

In some embodiments of the present invention, the time-division duplexmode includes a frame including a plurality of slots. At least a firstone of the slots is used to transmit wireless communications to theradiotelephones over the downlink satellite radiotelephone frequency. Atleast a second one of the slots is used to receive wirelesscommunications from the radiotelephones over the downlink satelliteradiotelephone frequency.

In still other embodiments, the downlink satellite radiotelephonefrequency comprises a downlink satellite radiotelephone frequency band.The ancillary terrestrial network is configured to transmit wirelesscommunications to, and receive wireless communications from, theradiotelephone over the downlink satellite radiotelephone frequency bandin a time-division duplex mode.

In yet other embodiments of the present invention, the time-divisionduplex mode employs a frame including a plurality of slots. A firstnumber of the slots is used to transmit wireless communications to theradiotelephones over the downlink satellite radiotelephone frequency. Asecond number of the slots is used to receive wireless communicationsfrom the radiotelephones over the downlink satellite radiotelephonefrequency. In some embodiments, the first number is greater than thesecond number.

In still other embodiments, at least a first one of the slots is used totransmit wireless communications to the radiotelephones over thedownlink satellite radiotelephone frequency a first modulation and/orprotocol such as EDGE modulation and/or protocol. At least a second oneof the slots is used to receive wireless communications from theradiotelephones over the downlink satellite radiotelephone frequencyusing a second modulation and/or protocol, such as GPRS modulationand/or protocol, that is less spectrally efficient than the firstmodulation and/or protocol.

It will be understood by those having skill in the art that the aboveembodiments have been described primarily with respect to a satelliteradiotelephone system that includes a space-based component and anancillary terrestrial network. However, other embodiments of theinvention can provide an ancillary terrestrial component, aradiotelephone and/or satellite radiotelephone communication methods forthe space-based component, the ancillary terrestrial network and/or theradiotelephones. Accordingly, a downlink satellite radiotelephonefrequency or frequencies can be reused terrestrially in a time-divisionduplex mode while reducing, minimizing or eliminating interference withspace-based use of the downlink satellite radiotelephone frequency orfrequencies.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of cellular radiotelephone systems andmethods according to embodiments of the invention.

FIG. 2 is a block diagram of adaptive interference reducers according toembodiments of the present invention.

FIG. 3 is a spectrum diagram that illustrates satellite L-band frequencyallocations.

FIG. 4 is a schematic diagram of cellular satellite systems and methodsaccording to other embodiments of the present invention.

FIG. 5 illustrates time-division duplex frame structures according toembodiments of the present invention.

FIG. 6 is a block diagram of architectures of ancillary terrestrialcomponents according to embodiments of the invention.

FIG. 7 is a block diagram of architectures of reconfigurableradiotelephones according to embodiments of the invention.

FIG. 8 graphically illustrates mapping of monotonically decreasing powerlevels to frequencies according to embodiments of the present invention.

FIG. 9 illustrates an ideal cell that is mapped to three power regionsand three associated carrier frequencies according to embodiments of theinvention.

FIG. 10 depicts a realistic cell that is mapped to three power regionsand three associated carrier frequencies according to embodiments of theinvention.

FIG. 11 illustrates two or more contiguous slots in a frame that areunoccupied according to embodiments of the present invention.

FIG. 12 illustrates loading of two or more contiguous slots with lowerpower transmissions according to embodiments of the present invention.

FIG. 13 is a schematic diagram of cellular satellite systems and methodsaccording to other embodiments of the present invention.

DETAILED DESCRIPTION

The present invention now will be described more fully hereinafter withreference to the accompanying drawings, in which typical embodiments ofthe invention are shown. This invention may, however, be embodied inmany different forms and should not be construed as limited to theembodiments set forth herein. Rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey the scope of the invention to those skilled in the art. Likenumbers refer to like elements throughout.

FIG. 1 is a schematic diagram of cellular satellite radiotelephonesystems and methods according to embodiments of the invention. As shownin FIG. 1, these cellular satellite radiotelephone systems and methods100 include at least one Space-Based Component (SBC) 110, such as asatellite. The space-based component 110 is configured to transmitwireless communications to a plurality of radiotelephones 120 a, 120 bin a satellite footprint comprising one or more satellite radiotelephonecells 130-130″″ over one or more satellite radiotelephone forward link(downlink) frequencies f_(D). The space-based component 110 isconfigured to receive wireless communications from, for example, a firstradiotelephone 120 a in the satellite radiotelephone cell 130 over asatellite radiotelephone return link (uplink) frequency f_(U). Anancillary terrestrial network, comprising at least one ancillaryterrestrial component 140, which may include an antenna 140 a and anelectronics system 140 b (for example, at least one antenna 140 a and atleast one electronics system 140 b), is configured to receive wirelesscommunications from, for example, a second radiotelephone 120 b in theradiotelephone cell 130 over the satellite radiotelephone uplinkfrequency, denoted f′_(U), which may be the same as f_(U). Thus, asillustrated in FIG. 1, radiotelephone 120 a may be communicating withthe space-based component 110 while radiotelephone 120 b may becommunicating with the ancillary terrestrial component 140. As shown inFIG. 1, the space-based component 110 also undesirably receives thewireless communications from the second radiotelephone 120 b in thesatellite radiotelephone cell 130 over the satellite radiotelephonefrequency f′_(U) as interference. More specifically, a potentialinterference path is shown at 150. In this potential interference path150, the return link signal of the second radiotelephone 120 b atcarrier frequency f′_(U) interferes with satellite communications. Thisinterference would generally be strongest when f′_(U)=f_(U), because, inthat case, the same return link frequency would be used for space-basedcomponent and ancillary terrestrial component communications over thesame satellite radiotelephone cell, and no spatial discriminationbetween satellite radiotelephone cells would appear to exist.

Still referring to FIG. 1, embodiments of satellite radiotelephonesystems/methods 100 can include at least one gateway 160 that caninclude an antenna 160 a and an electronics system 160 b that can beconnected to other networks 162 including terrestrial and/or otherradiotelephone networks. The gateway 160 also communicates with thespace-based component 110 over a satellite feeder link 112. The gateway160 also communicates with the ancillary terrestrial component 140,generally over a terrestrial link 142.

Still referring to FIG. 1, an Interference Reducer (IR) 170 a also maybe provided at least partially in the ancillary terrestrial componentelectronics system 140 b. Alternatively or additionally, an interferencereducer 170 b may be provided at least partially in the gatewayelectronics system 160 b. In yet other alternatives, the interferencereducer may be provided at least partially in other components of thecellular satellite system/method 100 instead of or in addition to theinterference reducer 170 a and/or 170 b. The interference reducer isresponsive to the space-based component 110 and to the ancillaryterrestrial component 140, and is configured to reduce the interferencefrom the wireless communications that are received by the space-basedcomponent 110 and is at least partially generated by the secondradiotelephone 120 b in the satellite radiotelephone cell 130 over thesatellite radiotelephone frequency f′_(U). The interference reducer 170a and/or 170 b uses the wireless communications f′_(U) that are intendedfor the ancillary terrestrial component 140 from the secondradiotelephone 120 b in the satellite radiotelephone cell 130 using thesatellite radiotelephone frequency f′_(U) to communicate with theancillary terrestrial component 140.

In embodiments of the invention, as shown in FIG. 1, the ancillaryterrestrial component 140 generally is closer to the first and secondradiotelephones 120 a and 120 b, respectively, than is the space-basedcomponent 110, such that the wireless communications from the secondradiotelephone 120 b are received by the ancillary terrestrial component140 prior to being received by the space-based component 110. Theinterference reducer 170 a and/or 170 b is configured to generate aninterference cancellation signal comprising, for example, at least onedelayed replica of the wireless communications from the secondradiotelephone 120 b that are received by the ancillary terrestrialcomponent 140, and to subtract the delayed replica of the wirelesscommunications from the second radiotelephone 120 b that are received bythe ancillary terrestrial component 140 from the wireless communicationsthat are received from the space-based component 110. The interferencereduction signal may be transmitted from the ancillary terrestrialcomponent 140 to the gateway 160 over link 142 and/or using otherconventional techniques.

Thus, adaptive interference reduction techniques may be used to at leastpartially cancel the interfering signal, so that the same, or othernearby, satellite radiotelephone uplink frequency can be used in a givencell for communications by radiotelephones 120 with the satellite 110and with the ancillary terrestrial component 140. Accordingly, allfrequencies that are assigned to a given cell 130 may be used for bothradiotelephone 120 communications with the space-based component 110 andwith the ancillary terrestrial component 140. Conventional systems mayavoid terrestrial reuse of frequencies within a given satellite cellthat are being used within the satellite cell for satellitecommunications. Stated differently, conventionally, only frequenciesused by other satellite cells may be candidates for terrestrial reusewithin a given satellite cell. Beam-to-beam spatial isolation that isprovided by the satellite system was relied upon to reduce or minimizethe level of interference from the terrestrial operations into thesatellite operations. In sharp contrast, embodiments of the inventioncan use an interference reducer to allow all frequencies assigned to asatellite cell to be used terrestrially and for satellite radiotelephonecommunications.

Embodiments of the invention according to FIG. 1 may arise from arealization that the return link signal from the second radiotelephone120 b at f_(U) generally will be received and processed by the ancillaryterrestrial component 140 much earlier relative to the time when it willarrive at the satellite gateway 160 from the space-based component 110via the interference path 150. Accordingly, the interference signal atthe satellite gateway 160 b can be at least partially canceled. Thus, asshown in FIG. 1, an interference cancellation signal, such as thedemodulated ancillary terrestrial component signal, can be sent to thesatellite gateway 160 b by the interference reducer 170 a in theancillary terrestrial component 140, for example using link 142. In theinterference reducer 170 b at the gateway 160 b, a weighted (inamplitude and/or phase) replica of the signal may be formed using, forexample, adaptive transversal filter techniques that are well known tothose having skill in the art. Then, a transversal filter output signalis subtracted from the aggregate received satellite signal at frequencyf′_(U) that contains desired as well as interference signals. Thus, theinterference cancellation need not degrade the signal-to-noise ratio ofthe desired signal at the gateway 160, because a regenerated(noise-free) terrestrial signal, for example as regenerated by theancillary terrestrial component 140, can be used to perform interferencesuppression.

FIG. 2 is a block diagram of embodiments of adaptive interferencecancellers that may be located in the ancillary terrestrial component140, in the gateway 160, and/or in another component of the cellularradiotelephone system 100. As shown in FIG. 2, one or more controlalgorithms 204, known to those having skill in the art, may be used toadaptively adjust the coefficients of a plurality of transversal filters202 a-202 n. Adaptive algorithms, such as Least Mean Square Error(LMSE), Kalman, Fast Kalman, Zero Forcing and/or various combinationsthereof or other techniques may be used. It will be understood by thosehaving skill in the art that the architecture of FIG. 2 may be used withan LMSE algorithm. However, it also will be understood by those havingskill in the art that conventional architectural modifications may bemade to facilitate other control algorithms.

Additional embodiments of the invention now will be described withreference to FIG. 3, which illustrates L-band frequency allocationsincluding cellular radiotelephone system forward links and return links.As shown in FIG. 3, the space-to-ground L-band forward link (downlink)frequencies are assigned from 1525 MHz to 1559 MHz. The ground-to-spaceL-band return link (uplink) frequencies occupy the band from 1626.5 MHzto 1660.5 MHz. Between the forward and return L-band links lie theGPS/GLONASS radionavigation band (from 1559 MHz to 1605 MHz).

In the detailed description to follow, GPS/GLONASS will be referred tosimply as GPS for the sake of brevity. Moreover, the acronyms ATC andSBC will be used for the ancillary terrestrial component and thespace-based component, respectively, for the sake of brevity.

As is known to those skilled in the art, GPS receivers may be extremelysensitive since they are designed to operate on very weakspread-spectrum radionavigation signals that arrive on the earth from aGPS satellite constellation. As a result, GPS receivers may to be highlysusceptible to in-band interference. ATCs that are configured to radiateL-band frequencies in the forward satellite band (1525 to 1559 MHz) canbe designed with very sharp out-of-band emissions filters to satisfy thestringent out-of-band spurious emissions desires of GPS.

Referring again to FIG. 1, some embodiments of the invention can providesystems and methods that can allow an ATC 140 to configure itself in oneof at least two modes. In accordance with a first mode, which may be astandard mode and may provide highest capacity, the ATC 140 transmits tothe radiotelephones 120 over the frequency range from 1525 MHz to 1559MHz, and receives transmissions from the radiotelephones 120 in thefrequency range from 1626.5 MHz to 1660.5 MHz, as illustrated in FIG. 3.In contrast, in a second mode of operation, the ATC 140 transmitswireless communications to the radiotelephones 120 over a modified rangeof satellite band forward link (downlink) frequencies. The modifiedrange of satellite band forward link frequencies may be selected toreduce, compared to the unmodified range of satellite band forward linkfrequencies, interference with wireless receivers such as GPS receiversthat operate outside the range of satellite band forward linkfrequencies.

Many modified ranges of satellite band forward link frequencies may beprovided according to embodiments of the present invention. In someembodiments, the modified range of satellite band forward linkfrequencies can be limited to a subset of the original range ofsatellite band forward link frequencies, so as to provide a guard bandof unused satellite band forward link frequencies. In other embodiments,all of the satellite band forward link frequencies are used, but thewireless communications to the radiotelephones are modified in a mannerto reduce interference with wireless receivers that operate outside therange of satellite band forward link frequencies. Combinations andsubcombinations of these and/or other techniques also may be used, aswill be described below.

It also will be understood that embodiments of the invention that willnow be described in connection with FIGS. 4-12 will be described interms of multiple mode ATCs 140 that can operate in a first standardmode using the standard forward and return links of FIG. 3, and in asecond or alternate mode that uses a modified range of satellite bandforward link frequencies and/or a modified range of satellite bandreturn link frequencies. These multiple mode ATCs can operate in thesecond, non-standard mode, as long as desirable, and can be switched tostandard mode otherwise. However, other embodiments of the presentinvention need not provide multiple mode ATCs but, rather, can provideATCs that operate using the modified range of satellite band forwardlink and/or return link frequencies.

Embodiments of the invention now will be described, wherein an ATCoperates with an SBC that is configured to receive wirelesscommunications from radiotelephones over a first range of satellite bandreturn link frequencies and to transmit wireless communications to theradiotelephones over a second range of satellite band forward linkfrequencies that is spaced apart from the first range. According tothese embodiments, the ATC is configured to use at least onetime-division duplex frequency to transmit wireless communications tothe radiotelephones and to receive wireless communications from theradiotelephones at different times. In particular, in some embodiments,the at least one time-division duplex frequency that is used to transmitwireless communications to the radiotelephones and to receive wirelesscommunications from the radiotelephones at different times, comprises aframe including a plurality of slots. At least a first one of the slotsis used to transmit wireless communications to the radiotelephones andat least a second one of the slots is used to receive wirelesscommunications from the radiotelephones. Thus, in some embodiments, theATC transmits and receives, in Time-division Duplex (TDD) mode, usingfrequencies from 1626.5 MHz to 1660.5 MHz. In some embodiments, all ATCsacross the entire network may have the statedconfiguration/reconfiguration flexibility. In other embodiments, onlysome ATCs may be reconfigurable.

FIG. 4 illustrates satellite systems and methods 400 according to someembodiments of the invention, including an ATC 140 communicating with aradiotelephone 120 b using a carrier frequency f″_(U) in TDD mode. FIG.5 illustrates an embodiment of a TDD frame structure. Assuming full-rateGSM (eight time slots per frame), up to four full-duplex voice circuitscan be supported by one TDD carrier. As shown in FIG. 5, the ATC 140transmits to the radiotelephone 120 b over, for example, time slotnumber 0. The radiotelephone 120 b receives and replies back to the ATC140 over, for example, time slot number 4. Time slots number 1 and 5 maybe used to establish communications with another radiotelephone, and soon.

A Broadcast Control CHannel (BCCH) is preferably transmitted from theATC 140 in standard mode, using a carrier frequency from below any guardband exclusion region. In other embodiments, a BCCH also can be definedusing a TDD carrier. In any of these embodiments, radiotelephones inidle mode can, per established GSM methodology, monitor the BCCH andreceive system-level and paging information. When a radiotelephone ispaged, the system decides what type of resource to allocate to theradiotelephone in order to establish the communications link. Whatevertype of resource is allocated for the radiotelephone communicationschannel (TDD mode or standard mode), the information is communicated tothe radiotelephone, for example as part of the call initializationroutine, and the radiotelephone configures itself appropriately.

It may be difficult for the TDD mode to co-exist with the standard modeover the same ATC, due, for example, to the ATC receiver LNA stage. Inparticular, assuming a mixture of standard and TDD mode GSM carriersover the same ATC, during the part of the frame when the TDD carriersare used to serve the forward link (when the ATC is transmitting TDD)enough energy may leak into the receiver front end of the same ATC todesensitize its LNA stage.

Techniques can be used to suppress the transmitted ATC energy over the1600 MHz portion of the band from desensitizing the ATC's receiver LNA,and thereby allow mixed standard mode and TDD frames. For example,isolation between outbound and inbound ATC front ends and/or antennasystem return loss may be increased or maximized. A switchableband-reject filter may be placed in front of the LNA stage. This filterwould be switched in the receiver chain (prior to the LNA) during thepart of the frame when the ATC is transmitting TDD, and switched outduring the rest of the time. An adaptive interference canceller can beconfigured at RF (prior to the LNA stage). If such techniques are used,suppression of the order of 70 dB can be attained, which may allow mixedstandard mode and TDD frames. However, the ATC complexity and/or costmay increase.

Thus, even though ATC LNA desensitization may be reduced or eliminated,it may use significant special engineering and attention and may not beeconomically worth the effort. Other embodiments, therefore, may keepTDD ATCs pure TDD, with the exception, perhaps, of the BCCH carrierwhich may not be used for traffic but only for broadcasting over thefirst part of the frame, consistent with TDD protocol. Moreover, RandomAccess CHannel (RACH) bursts may be timed so that they arrive at the ATCduring the second half of the TDD frame. In some embodiments, all TDDATCs may be equipped to enable reconfiguration in response to a command.

It is well recognized that during data communications or otherapplications, the forward link may use transmissions at higher ratesthan the return link. For example, in web browsing with aradiotelephone, mouse clicks and/or other user selections typically aretransmitted from the radiotelephone to the system. The system, however,in response to a user selection, may have to send large data files tothe radiotelephone. Hence, other embodiments of the invention may beconfigured to enable use of an increased or maximum number of time slotsper forward GSM carrier frame, to provide a higher downlink data rate tothe radiotelephones.

Thus, when a carrier frequency is configured to provide service in TDDmode, a decision may be made as to how many slots will be allocated toserving the forward link, and how many will be dedicated to the returnlink. Whatever the decision is, it may be desirable that it be adheredto by all TDD carriers used by the ATC, in order to reduce or avoid theLNA desensitization problem described earlier. In voice communications,the partition between forward and return link slots may be made in themiddle of the frame as voice activity typically is statisticallybidirectionally symmetrical. Hence, driven by voice, the center of theframe may be where the TDD partition is drawn.

To increase or maximize forward link throughput in data mode, data modeTDD carriers according to embodiments of the invention may use a morespectrally efficient modulation and/or protocol, such as the EDGEmodulation and/or protocol, on the forward link slots. The return linkslots may be based on a less spectrally efficient modulation and/orprotocol such as the GPRS (GMSK) modulation and/or protocol. The EDGEmodulation/protocol and the GPRS modulation/protocol are well known tothose having skill in the art, and need not be described further herein.Given an EDGE forward/GPRS return TDD carrier strategy, up to(384/2)=192 kbps may be supported on the forward link while on thereturn link the radiotelephone may transmit at up to (115/2)≈64 kbps.

In other embodiments, it also is possible to allocate six time slots ofan eight-slot frame for the forward link and only two for the returnlink. In these embodiments, for voice services, given the statisticallysymmetric nature of voice, the return link vocoder may need to becomparable with quarter-rate GSM, while the forward link vocoder canoperate at full-rate GSM, to yield six full-duplex voice circuits perGSM TDD-mode carrier (a voice capacity penalty of 25%). Subject to thisnon-symmetrical partitioning strategy, data rates of up to(384)(6/8)=288 kbps may be achieved on the forward link, with up to(115)(2/8)≈kbps on the return link.

FIG. 6 depicts an ATC architecture according to embodiments of theinvention, which can lend itself to automatic configuration between thetwo modes of standard GSM and TDD GSM on command, for example, from aNetwork Operations Center (NOC) via a Base Station Controller (BSC). Itwill be understood that in these embodiments, an antenna 620 cancorrespond to the antenna 140 a of FIGS. 1 and 4, and the remainder ofFIG. 6 can correspond to the electronics system 140 b of FIGS. 1 and 4.If a reconfiguration command for a particular carrier, or set ofcarriers, occurs while the carrier(s) are active and are supportingtraffic, then, via the in-band signaling Fast Associated Control CHannel(FACCH), all affected radiotelephones may be notified to alsoreconfigure themselves and/or switch over to new resources. Ifcarrier(s) are reconfigured from TDD mode to standard mode, automaticreassignment of the carrier(s) to the appropriate standard-mode ATCs,based, for example, on capacity demand and/or reuse pattern can beinitiated by the NOC. If, on the other hand, carrier(s) are reconfiguredfrom standard mode to TDD mode, automatic reassignment to theappropriate TDD-mode ATCs can take place on command from the NOC.

Still referring to FIG. 6, a switch 610 may remain closed when carriersare to be demodulated in the standard mode. In TDD mode, this switch 610may be open during the first half of the frame, when the ATC istransmitting, and closed during the second half of the frame, when theATC is receiving. Other embodiments also may be provided.

FIG. 6 assumes N transceivers per ATC sector, where N can be as small asone, since a minimum of one carrier per sector generally is desired.Each transceiver is assumed to operate over one GSM carrier pair (whenin standard mode) and can thus support up to eight full-duplex voicecircuits, neglecting BCCH channel overhead. Moreover, a standard GSMcarrier pair can support sixteen full-duplex voice circuits when inhalf-rate GSM mode, and up to thirty two full-duplex voice circuits whenin quarter-rate GSM mode.

When in TDD mode, the number of full duplex voice circuits may bereduced by a factor of two, assuming the same vocoder. However, in TDDmode, voice service can be offered via the half-rate GSM vocoder withalmost imperceptible quality degradation, in order to maintain invariantvoice capacity. FIG. 7 is a block diagram of a reconfigurableradiotelephone architecture that can communicate with a reconfigurableATC architecture of FIG. 6. In FIG. 7, an antenna 720 is provided, andthe remainder of FIG. 7 can provide embodiments of an electronics systemfor the radiotelephone.

It will be understood that the ability to reconfigure ATCs andradiotelephones according to embodiments of the invention may beobtained at a relatively small increase in cost. The cost may be mostlyin Non-Recurring Engineering (NRE) cost to develop software. Somerecurring cost may also be incurred, however, in that at least anadditional RF filter and a few electronically controlled switches may beused per ATC and radiotelephone. All other hardware/software can becommon to standard-mode and TDD-mode GSM.

Referring now to FIG. 8, other radiotelephone systems and methodsaccording to embodiments of the invention now will be described. Inthese embodiments, the modified second range of satellite band forwardlink frequencies includes a plurality of frequencies in the second rangeof satellite band forward link frequencies that are transmitted by theATCs to the radiotelephones at a power level, such as maximum powerlevel, that monotonically decreases as a function of (increasing)frequency. More specifically, as will be described below, in someembodiments, the modified second range of satellite band forward linkfrequencies includes a subset of frequencies proximate to a first orsecond end of the range of satellite band forward link frequencies thatare transmitted by the ATC to the radiotelephones at a power level, suchas a maximum power level, that monotonically decreases toward the firstor second end of the second range of satellite band forward linkfrequencies. In still other embodiments, the first range of satelliteband return link frequencies is contained in an L-band of satellitefrequencies above GPS frequencies and the second range of satellite bandforward link frequencies is contained in the L-band of satellitefrequencies below the GPS frequencies. The modified second range ofsatellite band forward link frequencies includes a subset of frequenciesproximate to an end of the second range of satellite band forward linkfrequencies adjacent the GPS frequencies that are transmitted by the ATCto the radiotelephones at a power level, such as a maximum power level,that monotonically decreases toward the end of the second range ofsatellite band forward link frequencies adjacent the GPS frequencies.

Without being bound by any theory of operation, a theoretical discussionof the mapping of ATC maximum power levels to carrier frequenciesaccording to embodiments of the present invention now will be described.Referring to FIG. 8, let ν=

(ρ) represent a mapping from the power (ρ) domain to the frequency (ν)range. The power (ρ) is the power that an ATC uses or should transmit inorder to reliably communicate with a given radiotelephone. This powermay depend on many factors such as the radiotelephone's distance fromthe ATC, the blockage between the radiotelephone and the ATC, the levelof multipath fading in the channel, etc., and as a result, will, ingeneral, change as a function of time. Hence, the power used generallyis determined adaptively (iteratively) via closed-loop power control,between the radiotelephone and ATC.

The frequency (ν) is the satellite carrier frequency that the ATC usesto communicate with the radiotelephone. According to embodiments of theinvention, the mapping

is a monotonically decreasing function of the independent variable ρ.Consequently, in some embodiments, as the maximum ATC power increases,the carrier frequency that the ATC uses to establish and/or maintain thecommunications link decreases. FIG. 8 illustrates an embodiment of apiece-wise continuous monotonically decreasing (stair-case) function.Other monotonic functions may be used, including linear and/ornonlinear, constant and/or variable decreases. FACCH or Slow AssociatedControl CHannel (SACCH) messaging may be used in embodiments of theinvention to facilitate the mapping adaptively and in substantially realtime.

FIG. 9 depicts an ideal cell according to embodiments of the invention,where, for illustration purposes, three power regions and threeassociated carrier frequencies (or carrier frequency sets) are beingused to partition a cell. For simplicity, one ATC transmitter at thecenter of the idealized cell is assumed with no sectorization. Inembodiments of FIG. 9, the frequency (or frequency set) f_(I) is takenfrom substantially the upper-most portion of the L-band forward linkfrequency set, for example from substantially close to 1559 MHz (seeFIG. 3). Correspondingly, the frequency (or frequency set) f_(M) istaken from substantially the central portion of the L-band forward linkfrequency set (see FIG. 3). In concert with the above, the frequency (orfrequency set) f_(O) is taken from substantially the lowest portion ofthe L-band forward link frequencies, for example close to 1525 MHz (seeFIG. 3).

Thus, according to embodiments of FIG. 9, if a radiotelephone is beingserved within the outer-most ring of the cell, that radiotelephone isbeing served via frequency f_(O). This radiotelephone, being within thefurthest area from the ATC, has (presumably) requested maximum (or nearmaximum) power output from the ATC. In response to the maximum (or nearmaximum) output power request, the ATC uses its a priori knowledge ofpower-to-frequency mapping, such as a three-step staircase function ofFIG. 9. Thus, the ATC serves the radiotelephone with a low-valuefrequency taken from the lowest portion of the mobile L-band forwardlink frequency set, for example, from as close to 1525 MHz as possible.This, then, can provide additional safeguard to any GPS receiver unitthat may be in the vicinity of the ATC.

Embodiments of FIG. 9 may be regarded as idealized because theyassociate concentric ring areas with carrier frequencies (or carrierfrequency sets) used by an ATC to serve its area. In reality, concentricring areas generally will not be the case. For example, a radiotelephonecan be close to the ATC that is serving it, but with significantblockage between the radiotelephone and the ATC due to a building. Thisradiotelephone, even though relatively close to the ATC, may alsorequest maximum (or near maximum) output power from the ATC. With thisin mind, FIG. 10 may depict a more realistic set of area contours thatmay be associated with the frequencies being used by the ATC to serveits territory, according to embodiments of the invention. The frequency(or frequency set) f_(I) may be reused in the immediately adjacent ATCcells owing to the limited geographical span associated with f_(I)relative to the distance between cell centers. This may also hold forf_(M).

Referring now to FIG. 11, other modified second ranges of satellite bandforward link frequencies that can be used by ATCs according toembodiments of the present invention now will be described. In theseembodiments, at least one frequency in the modified second range ofsatellite band forward link frequencies that is transmitted by the ATCto the radiotelephones comprises a frame including a plurality of slots.In these embodiments, at least two contiguous slots in the frame that istransmitted by the ATC to the radiotelephones are left unoccupied. Inother embodiments, three contiguous slots in the frame that istransmitted by the ATC to the radiotelephones are left unoccupied. Inyet other embodiments, at least two contiguous slots in the frame thatis transmitted by the ATC to the radiotelephones are transmitted atlower power than remaining slots in the frame. In still otherembodiments, three contiguous slots in the frame that is transmitted bythe ATC to the radiotelephones are transmitted at lower power thanremaining slots in the frame. In yet other embodiments, the lower powerslots may be used with first selected ones of the radiotelephones thatare relatively close to the ATC and/or are experiencing relatively smallsignal blockage, and the remaining slots are transmitted at higher powerto second selected ones of the radiotelephones that are relatively farfrom the ATC and/or are experiencing relatively high signal blockage.

Stated differently, in accordance with some embodiments of theinvention. only a portion of the TDMA frame is utilized. For example,only the first four (or last four, or any contiguous four) time slots ofa full-rate GSM frame are used to support traffic. The remaining slotsare left unoccupied (empty). In these embodiments, capacity may be lost.However, as has been described previously, for voice services, half-rateand even quarter-rate GSM may be invoked to gain capacity back, withsome potential degradation in voice quality. The slots that are notutilized preferably are contiguous, such as slots 0 through 3 or 4through 7 (or 2 through 5, etc.). The use of non-contiguous slots suchas 0, 2, 4, and 6, for example, may be less desirable. FIG. 11illustrates four slots (4-7) being used and four contiguous slots (0-3)being empty in a GSM frame.

It has been found experimentally, according to these embodiments of theinvention, that GPS receivers can perform significantly better when theinterval between interference bursts is increased or maximized. Withoutbeing bound by any theory of operation, this effect may be due to therelationship between the code repetition period of the GPS C/A code (1msec.) and the GSM burst duration (about 0.577 msec.). With a GSM frameoccupancy comprising alternate slots, each GPS signal code period canexperience at least one “hit”, whereas a GSM frame occupancy comprisingfour to five contiguous slots allows the GPS receiver to derivesufficient clean information so as to “flywheel” through the errorevents.

According to other embodiments of the invention, embodiments of FIGS.8-10 can be combined with embodiments of FIG. 11. Furthermore, accordingto other embodiments of the invention, if an f_(I) carrier of FIGS. 9 or10 is underutilized, because of the relatively small footprint of theinner-most region of the cell, it may be used to support additionaltraffic over the much larger outermost region of the cell.

Thus, for example, assume that only the first four slots in each frameof ft are being used for inner region traffic. In embodiments of FIGS.8-10, these four f_(I) slots are carrying relatively low power bursts,for example of the order of 100 mW or less, and may, therefore, appearas (almost) unoccupied from an interference point of view. Loading theremaining four (contiguous) time slots of f_(I) with relativelyhigh-power bursts may have negligible effect on a GPS receiver becausethe GPS receiver would continue to operate reliably based on the benigncontiguous time interval occupied by the four low-power GSM bursts. FIG.12 illustrates embodiments of a frame at carrier f_(I) supporting fourlow-power (inner interval) users and four high-power (outer interval)users. In fact, embodiments illustrated in FIG. 12 may be a preferredstrategy for the set of available carrier frequencies that are closestto the GPS band. These embodiments may avoid undue capacity loss by morefully loading the carrier frequencies.

The experimental finding that interference from GSM carriers can berelatively benign to GPS receivers provided that no more than, forexample, 5 slots per 8 slot GSM frame are used in a contiguous fashioncan be very useful. It can be particularly useful since thisexperimental finding may hold even when the GSM carrier frequency isbrought very close to the GPS band (as close as 1558.5 MHz) and thepower level is set relatively high. For example, with five contiguoustime slots per frame populated, the worst-case measured GPS receiver mayattain at least 30 dB of desensitization margin, over the entire ATCservice area, even when the ATC is radiating at 1558.5 MHz. With fourcontiguous time slots per frame populated, an additional 10 dBdesensitization margin may be gained for a total of 40 dB for theworst-case measured GPS receiver, even when the ATC is radiating at1558.5 MHz.

There still may be concern about the potential loss in network capacity(especially in data mode) that may be incurred over the frequencyinterval where embodiments of FIG. 11 are used to underpopulate theframe. Moreover, even though embodiments of FIG. 12 can avoid capacityloss by fully loading the carrier, they may do so subject to theconstraint of filling up the frame with both low-power and high-powerusers. Moreover, if forward link carriers are limited to 5 contiguoushigh power slots per frame, the maximum forward link data rate percarrier that may be aimed at a particular user may becomeproportionately less.

Therefore, in other embodiments, carriers which are subject tocontiguous empty/low power slots are not used for the forward link.Instead, they are used for the return link. Consequently, in someembodiments, at least part of the ATC is configured in reverse frequencymode compared to the SBC in order to allow maximum data rates over theforward link throughout the entire network. On the reverse frequencyreturn link, a radiotelephone may be limited to a maximum of 5 slots perframe, which can be adequate for the return link. Whether the fiveavailable time slots per frame, on a reverse frequency return linkcarrier, are assigned to one radiotelephone or to five differentradiotelephones, they can be assigned contiguously in these embodiments.As was described in connection with FIG. 12, these five contiguous slotscan be assigned to high-power users while the remaining three slots maybe used to serve low-power users.

Other embodiments may be based on operating the ATC entirely in reversefrequency mode compared to the SBC. In these embodiments, an ATCtransmits over the satellite return link frequencies whileradiotelephones respond over the satellite forward link frequencies. Ifsufficient contiguous spectrum exists to support CDMA technologies, andin particular the emerging Wideband-CDMA 3G standard, the ATC forwardlink can be based on Wideband-CDMA to increase or maximize datathroughput capabilities. Interference with GPS may not be an issue sincethe ATCs transmit over the satellite return link in these embodiments.Instead, interference may become a concern for the radiotelephones.Based, however, on embodiments of FIGS. 11-12, the radiotelephones canbe configured to transmit GSM since ATC return link rates are expected,in any event, to be lower than those of the forward link, Accordingly,the ATC return link may employ GPRS-based data modes, possibly evenEDGE. Thus, return link carriers that fall within a predeterminedfrequency interval from the GPS band-edge of 1559 MHz, can be underloaded, per embodiments of FIGS. 11 or 12, to satisfy GPS interferenceconcerns.

Finally, other embodiments may use a partial or total reverse frequencymode and may use CDMA on both forward and return links. In theseembodiments, the ATC forward link to the radiotelephones utilizes thefrequencies of the satellite return link (1626.5 MHz to 1660.5 MHz)whereas the ATC return link from the radiotelephones uses thefrequencies of the satellite forward link (1525 MHz to 1559 MHz). TheATC forward link can be based on an existing or developing CDMAtechnology (e.g., IS-95, Wideband-CDMA, etc.). The ATC network returnlink can also be based on an existing or developing CDMA technologyprovided that the radiotelephone's output is gated to ceasetransmissions for approximately 3 msec once every T msec. In someembodiments, T will be greater than or equal to 6 msec.

This gating may not be needed for ATC return link carriers atapproximately 1550 MHz or below. This gating can reduce or minimizeout-of-band interference (desensitization) effects for GPS receivers inthe vicinity of an ATC. To increase the benefit to GPS, the gatingbetween all radiotelephones over an entire ATC service area can besubstantially synchronized. Additional benefit to GPS may be derivedfrom system-wide synchronization of gating. The ATCs can instruct allactive radiotelephones regarding the gating epoch. All ATCs can bemutually synchronized via GPS.

Terrestrial Reuse of Cellular Satellite Frequency Spectrum inTime-division Duplex Mode

FIG. 13 is a schematic diagram of cellular satellite systems and methodsaccording to other embodiments of the present invention, in which adownlink satellite radiotelephone frequency or frequencies isterrestrially reused by an ancillary terrestrial network in alime-Division Duplex (TDD) mode. In particular, FIG. 13 illustratessatellite systems and methods 1300 according to some embodiments of theinvention, including an ATC 140 communicating with a radiotelephone 120b using a downlink carrier frequency f_(D) in TDD mode.

More specifically, these satellite radiotelephone systems and methods1300 include a space-based component 110 that is configured to receivewireless communications from radiotelephones, such as the radiotelephone120 a, in a satellite footprint 130 over an uplink satelliteradiotelephone frequency f_(U) and to transmit wireless communicationsto the radiotelephones, such as the radiotelephone 120 a, over adownlink satellite radiotelephone frequency f_(D). An ancillaryterrestrial network including at least one ancillary terrestrialcomponent 140 is configured to transmit wireless communications to, andreceive wireless communications from, the radiotelephones, such as theradiotelephone 120 b, over the downlink satellite radiotelephonefrequency f_(D) in a time-division duplex mode.

These embodiments of the invention may arise from a recognition that ifa downlink satellite radiotelephone frequency f_(D) is reusedterrestrially in time-division duplex mode, bidirectional communicationsbetween the ATC 140 and the radiotelephones 120 may be provided withoutgenerating a potential interference path with space-based communicationsat the satellite 110 and/or the gateway 160. Stated differently,comparing FIGS. 4 and 13, the potential interference path 150 of FIG. 4can be reduced and, in some embodiments, eliminated, by using thedownlink satellite radiotelephone frequency f_(D) for time-divisionduplex communications between the ATC 140 and the radiotelephones 120.

In other embodiments of the present invention, the ancillary terrestrialnetwork also may be configured to transmit wireless communications to,and receive wireless communications from, the radiotelephones over theuplink satellite radiotelephone frequency f_(U) in a time-divisionduplex mode, as was already described in FIG. 4. Thus, some embodimentsof the present invention can combine FIGS. 4 and 13 for time-divisionduplex terrestrial reuse of uplink and downlink satellite radiotelephonefrequencies. Other embodiments of the invention may also providedspace-based communications with the radiotelephones using the uplinksatellite radiotelephone frequency f_(U) and/or the downlink satelliteradiotelephone frequency f_(D) in a time-division duplex mode,

Various embodiments of TDD modes may be provided according toembodiments of the present invention, similar to the modes which werealready described in connection with FIG. 4. In some embodiments, thetime-division duplex mode includes a frame, for example as was describedin FIG. 5, including a plurality of slots. At least a first one of theslots is used to transmit wireless communications to the radiotelephonesover the downlink satellite radiotelephone frequency f_(D), and at leastone of the slots is used to receive wireless communications from theradiotelephones over the downlink satellite radiotelephone frequencyf_(D).

In still other embodiments, more than one downlink satelliteradiotelephone carrier frequency f_(D) may be used in a TDD mode. Thus,in some embodiments, the entire downlink radiotelephone frequency bandmay be used to transmit wireless communications to, and receive wirelesscommunications from, the radiotelephones in a time-division duplex mode.A portion of the downlink radiotelephone frequency band also may be usedin TDD mode in other embodiments of the present invention.

Moreover, as also was described in connection with FIG. 4 above, duringdata communications or other applications, the downlink may usetransmissions at higher rates than the uplink. Hence, other embodimentsof the present invention may be configured to enable asymmetrical use ofthe time slots, to provide a higher downlink data rate to theradiotelephones. Thus, as was described above in connection with FIG. 4,a first number of the slots may be used to transmit wirelesscommunications to the radiotelephones over the downlink satelliteradiotelephone frequency, and a second number of the slots may be usedto receive wireless communications from the radiotelephones over thedownlink satellite radiotelephone frequency, wherein the first number isgreater than the second number. In other embodiments, at least a firstone of the slots is used to transmit wireless communications to theradiotelephones over the downlink satellite radiotelephone frequencyusing EDGE modulation and/or protocol, and at least a second one of theslots is used to receive wireless communications from theradiotelephones over the downlink satellite radiotelephone frequencyusing GPRS modulation and/or protocol. Moreover, in other embodiments,at least a first one of the slots is used to transmit wirelesscommunications to the radiotelephones over the downlink satelliteradiotelephone frequency using a first modulation and/or protocol, andat least a second one of the slots is used to receive wirelesscommunications from the radiotelephones over the downlink satelliteradiotelephone frequency using a second modulation and/or protocol,wherein the first modulation and/or protocol is more spectrallyefficient than the second modulation and/or protocol.

Accordingly, embodiments of the present invention can terrestriallyreuse some or all of the downlink satellite radiotelephone frequenciesin a time-division duplex mode, to reduce or eliminate interference bythe radiotelephones and/or ancillary terrestrial components, withspace-based communications at the satellite and/or satellite gateway. Aninterference reducer may not need to be employed in some embodiments ofthe present invention, because the frequencies generated by theradiotelephones and/or the ATCs may only be satellite radiotelephonedownlink frequencies.

In the drawings and specification, there have been disclosed typicalpreferred embodiments of the invention and, although specific terms areemployed, they are used in a generic and descriptive sense only and notfor purposes of limitation, the scope of the invention being set forthin the following claims.

1. A satellite radiotelephone system comprising: a space-based componentthat is configured to receive wireless communications fromradiotelephones in a satellite footprint over an uplink satelliteradiotelephone frequency and to transmit wireless communications toradiotelephones over a downlink satellite radiotelephone frequency; andan ancillary terrestrial network that is configured to transmit wirelesscommunications to, and receive wireless communications from,radiotelephones over the downlink satellite radiotelephone frequency ina time-division duplex mode.
 2. A satellite radiotelephone systemaccording to claim 1 wherein the ancillary terrestrial network also isconfigured to transmit wireless communications to, and receive wirelesscommunications from, radiotelephones over the uplink satelliteradiotelephone frequency in a time-division duplex mode.
 3. A satelliteradiotelephone system according to claim 1 wherein the time-divisionduplex mode includes a frame including a plurality of slots, wherein atleast a first one of the slots is used to transmit wirelesscommunications to radiotelephones over the downlink satelliteradiotelephone frequency and wherein at least a second one of the slotsis used to receive wireless communications from radiotelephones over thedownlink satellite radiotelephone frequency.
 4. A satelliteradiotelephone system according to claim 1 wherein the downlinksatellite radiotelephone frequency comprises a downlink satelliteradiotelephone frequency band and wherein the ancillary terrestrialnetwork is configured to transmit wireless communications to, andreceive wireless communications from, radiotelephones over the downlinksatellite radiotelephone frequency band in a time-division duplex mode.5. A satellite radiotelephone system according to claim 1 wherein thetime-division duplex mode includes a frame including a plurality ofslots, wherein a first number of the slots is used to transmit wirelesscommunications to radiotelephones over the downlink satelliteradiotelephone frequency and wherein a second number of the slots isused to receive wireless communications from radiotelephones over thedownlink satellite radiotelephone frequency, wherein the first number isgreater than the second number.
 6. A satellite radiotelephone systemaccording to claim 1 wherein the time-division duplex mode includes aframe including a plurality of slots, wherein at least a first one ofthe slots is used to transmit wireless communications to radiotelephonesover the downlink satellite radiotelephone frequency using EDGEmodulation and/or protocol and wherein at least a second one of theslots is used to receive wireless communications from radiotelephonesover the downlink satellite radiotelephone frequency using GPRSmodulation and/or protocol.
 7. A satellite radiotelephone systemaccording to claim 1 wherein the time-division duplex mode includes aframe including a plurality of slots, wherein at least a first one ofthe slots is used to transmit wireless communications to radiotelephonesover the downlink satellite radiotelephone frequency using a firstmodulation and/or protocol and wherein at least a second one of theslots is used to receive wireless communications from radiotelephonesover the downlink satellite radiotelephone frequency using a secondmodulation and/or protocol, wherein the first modulation and/or protocolis more spectrally efficient than the second modulation and/or protocol.8. An ancillary terrestrial component for a satellite radiotelephonesystem that includes a space-based component that is configured toreceive wireless communications from radiotelephones in a satellitefootprint over an uplink satellite radiotelephone frequency and totransmit wireless communications to radiotelephones over a downlinksatellite radiotelephone frequency, the ancillary terrestrial componentcomprising: an electronics system that is configured to transmitwireless communications to, and receive wireless communications from,radiotelephones over the downlink satellite radiotelephone frequency ina time-division duplex mode.
 9. An ancillary terrestrial componentaccording to claim 8 wherein the electronics system also is configuredto transmit wireless communications to, and receive wirelesscommunications from, radiotelephones over the uplink satelliteradiotelephone frequency in a time-division duplex mode.
 10. Anancillary terrestrial component according to claim 8 wherein thetime-division duplex mode includes a frame including a plurality ofslots, wherein at least a first one of the slots is used to transmitwireless communications to radiotelephones over the downlink satelliteradiotelephone frequency and wherein at least a second one of the slotsis used to receive wireless communications from radiotelephones over thedownlink satellite radiotelephone frequency.
 11. An ancillaryterrestrial component according to claim 8 wherein the downlinksatellite radiotelephone frequency comprises a downlink satelliteradiotelephone frequency band and wherein the electronics system isconfigured to transmit wireless communications to, and receive wirelesscommunications from, radiotelephones over the downlink satelliteradiotelephone frequency band in a time-division duplex mode.
 12. Anancillary terrestrial component according to claim 8 wherein thetime-division duplex mode includes a frame including a plurality ofslots, wherein a first number of the slots is used to transmit wirelesscommunications to radiotelephones over the downlink satelliteradiotelephone frequency and wherein a second number of the slots isused to receive wireless communications from radiotelephones over thedownlink satellite radiotelephone frequency, wherein the first number isgreater than the second number.
 13. An ancillary terrestrial componentaccording to claim 8 wherein the time-division duplex mode includes aframe including a plurality of slots, wherein at least a first one ofthe slots is used to transmit wireless communications to radiotelephonesover the downlink satellite radiotelephone frequency using EDGEmodulation and/or protocol and wherein at least a second one of theslots is used to receive wireless communications from radiotelephonesover the downlink satellite radiotelephone frequency using GPRSmodulation and/or protocol.
 14. An ancillary terrestrial componentaccording to claim 8 wherein the time-division duplex mode includes aframe including a plurality of slots, wherein at least a first one ofthe slots is used to transmit wireless communications to radiotelephonesover the downlink satellite radiotelephone frequency using a firstmodulation and/or protocol and wherein at least a second one of theslots is used to receive wireless communications from radiotelephonesover the downlink satellite radiotelephone frequency using a secondmodulation and/or protocol, wherein the first modulation and/or protocolis more spectrally efficient than the second modulation and/or protocol.15. A satellite radiotelephone communication method comprising:receiving wireless communications at a space-based component fromradiotelephones in a satellite footprint over an uplink satelliteradiotelephone frequency; transmitting wireless communications from thespace-based component to radiotelephones over a downlink radiotelephonefrequency; and transmitting wireless communications from an ancillaryterrestrial network to radiotelephones and transmitting wirelesscommunications from radiotelephones to the ancillary terrestrial networkover the downlink satellite radiotelephone frequency in a time-divisionduplex mode.
 16. A method according to claim 15 further comprising:transmitting wireless communications from the ancillary terrestrialnetwork to radiotelephones and transmitting wireless communications fromradiotelephones to the ancillary terrestrial network over uplinksatellite radiotelephone frequency in a time-division duplex mode.
 17. Amethod according to claim 15 wherein the time-division duplex modeincludes a frame including a plurality of slots, wherein at least afirst one of the slots is used to transmit wireless communications fromthe ancillary terrestrial network to radiotelephones over the downlinksatellite radiotelephone frequency and wherein at least a second one ofthe slots is used to transmit wireless communications fromradiotelephones to the ancillary terrestrial network over the downlinksatellite radiotelephone frequency.
 18. A method according to claim 15wherein the downlink satellite radiotelephone frequency comprises adownlink satellite radiotelephone frequency band and wherein the methodfurther comprises transmitting wireless communications from theancillary terrestrial network to radiotelephones and transmittingwireless communications from radiotelephones to the ancillaryterrestrial network over the downlink satellite radiotelephone frequencyband in a time-division duplex mode.
 19. A method according to claim 15wherein the time-division duplex mode includes a frame including aplurality of slots, wherein a first number of the slots is used totransmit wireless communications from the ancillary terrestrial networkto radiotelephones over the downlink satellite radiotelephone frequencyand wherein a second number of the slots is used to transmit wirelesscommunications from radiotelephones to the ancillary terrestrial networkover the downlink satellite radiotelephone frequency, wherein the firstnumber is greater than the second number.
 20. A method according toclaim 15 wherein the time-division duplex mode includes a frameincluding a plurality of slots, wherein at least a first one of theslots is used to transmit wireless communications from the ancillaryterrestrial network to radiotelephones over the downlink satelliteradiotelephone frequency using EDGE modulation and/or protocol andwherein at least a second one of the slots is used to transmit wirelesscommunications from radiotelephones to the ancillary terrestrial networkover the downlink satellite radiotelephone frequency using GPRSmodulation and/or protocol.
 21. A method according to claim 15 whereinthe time-division duplex mode includes a frame including a plurality ofslots, wherein at least a first one of the slots is used to transmitwireless communications from the ancillary terrestrial network toradiotelephones over the downlink satellite radiotelephone frequencyusing a first modulation and/or protocol and wherein at least a secondone of the slots is used to transmit wireless communications fromradiotelephones to the ancillary terrestrial network over the downlinksatellite radiotelephone frequency using a second modulation and/orprotocol, wherein the first modulation and/or protocol is morespectrally efficient than the second modulation and/or protocol.